The present invention concerns a device for measuring the gap width between two structural components, wherein the gap is delimited by the edges of the structural components, comprising
illumination means for illuminating the structural components;
detection means for detecting reflections from the structural components in the area of the gap caused by the illumination means; and
evaluation means for evaluating the detected reflections and for determining the width of the gap.
The invention also concerns a gap measuring arrangement for measuring the width of gaps between the leaves or the rest of the body of a vehicle, wherein the gaps are limited by edges of the leaves and/or the rest of the body.
Finally, the invention concerns a method for measuring the gap width between two structural components, the gap being delimited by the edges of the structural components, wherein
the structural components are illuminated by illumination means;
the reflections, generated by the illumination means on the structural components in the area of the gap are detected;
the detected reflections are evaluated and
the width of the gap is determined.
Devices of the above mentioned kind are used in various fields. Such devices are widely used e.g. in the automotive industry for measuring the width of gaps between the leaves or the rest of the body of a vehicle. The gaps are delimited either from both sides by edges of the leaves or from one side by an edge of a leaf and by the rest of the body at the other side. In the following, leaves designate parts of the body of a vehicle hinged in a pivotable fashion to the rest of the body. In the case of an automotive vehicle, these are, in particular, the doors, the hood and the trunk.
During manufacture of a vehicle, the correct position and location of the leaves relative to the rest of the body is checked several times. Directly after mounting of the leaves, one examines e.g. whether or not the leaves are properly fitted to the rest of the body. The first check is performed before the body is painted. Depending on the material from which the body is made, the body has a mat, untreated steel, aluminium or plastic surface. These different surface materials have widely varying reflection characteristics. The normally mat body surface reflects light poorly.
During final inspection of the vehicle, the gap width between the leaves or the rest of the body is again examined at a plurality of measuring points. For this final examination, the body has been painted. Depending on the color of the paint, the body surface has differing reflection properties.
Various conventional devices and methods have been used for measuring the gap width. Due to their easy handling and high measurement speed, feeler gauges of differing widths have become established in the automotive industry. By inserting various feeler gauges into the gap, that feeler gauge is determined which precisely fits into the gap. From the width of this feeler gauge, one obtains the width of the gap. The measurement results which can be achieved with this method, are not very accurate. With gap widths in the range of less than 10 mm, the measurement result depends e.g. on the angle at which the feeler gauge is introduced into the gap.
Moreover, the measurement results which can be achieved with this method are not reproducible. With this method, different individuals obtain different measurement results for the same gap. Different automotive vehicle manufacturers measure the gap width of their vehicles at different measuring points and in different ways. For this reason, different automotive vehicle manufacturers may obtain completely different measurement results for identical gap widths. The measurement value of the gap width between the leaves or the rest of the body obtained with the conventional method can therefore not be used as a comparative value for assessment of the production qualities of various automobile manufacturers.
Prior art discloses a further method of measuring the gap width between two structural components, referred to as edge detection, wherein the gap is delimited by the edges of the structural components. In this method, illumination means illuminate the structural components in the area of the gap. Illumination of the structural components causes strong surface reflections on the surfaces of the structural components. The gap absorbs the light emitted by the illumination means. Detection means detect the light/dark transition on one side of the gap and the dark/light transition on the other side of the gap. Evaluation means evaluate the detected reflections and determine the width of the gap.
This conventional method can function with sufficient accuracy only if the light/dark transition or the dark/light transition is clearly visible and can be clearly detected by the detection means. This requires relatively good reflection properties of the surfaces of the structural components. Such good reflection properties can only be effected by very smooth surfaces. Reflections from untreated metal surfaces are too weak for this method. Towards this end, the edge detection method cannot be used for checking proper fitting of the leaves to the rest of the body.
In addition, the surfaces have different reflection properties in dependence on their color. The conventional edge detection method thereby produces different measurement results for the same gap width, in dependence on the color of the surface of the structural components defining the gap. Since vehicle body are painted in a large number of different colors, the conventional edge detection method cannot be used in the automotive industry for final inspection to check the width of gaps between the leaves and the rest of the body parts of a vehicle.
It is therefore the underlying purpose of the present invention to design and further develop a device of the above mentioned kind in such a manner that the gap width between two structural components can be measured in a simple, reliable, accurate, and reproducible manner independently of the surface finish of the structural components.
Departing from the device of the above mentioned kind, this object is achieved in accordance with the invention by disposing and orienting the illumination means and the detection means relative to one another and relative to the gap such that the detection means detect line-shaped reflections on the edges of the structural components delimiting the gap.
With the device in accordance with the invention, the line-shaped reflections are detected at the edges of the structural components delimiting the gap. The illumination means must therefore be disposed and oriented relative to the gap in such a manner, that at least part of the light beams emitted by the illumination means is reflected as line-shaped reflections at the edges of the structural components. The detection means must be disposed and oriented relative to the gap such that they can detect these line-shaped reflections. In addition, the illumination means and the detection means must be disposed relative to the structural components in such a manner that the detection means do not detect a virtual reflected image of the illumination means.
The detection means detect the line-shaped reflections at the edges of the structural components. More precisely, they detect a dark/light/dark transition between the structural component (dark), the line-shaped reflection (light), and the gap (dark), or vice versa. The line-shaped reflections are generated at edges having an edge radius which may be very small. The line-shaped reflections occur even with relatively sharp-edged edges. The line-shaped reflections also occur for relatively poorly reflecting surfaces such as mat untreated metal surfaces. The position of the line-shaped reflections at the edges does not depend on the reflection properties of the surface.
The device in accordance with the invention permits measurement of the gap width between two structural components in a simple, reliable, precise and reproducible manner. It is particularly suited for use in the automotive industry for measurement of the width of gaps between leaves or the rest of the body of a vehicle. The device in accordance with the invention provides measuring results of high accuracy, independent of the color of the body. It can be easily used to check proper fitting of the leaves into the rest of the body or for a final check of the gap width between the leaves and the rest of the body parts of a vehicle.
In addition to measurement of the gap width and of the mismatch between the structural components defining the gap, the device in accordance with the invention can also measure the travel of a gap. Since the device in accordance with the invention effects measurements using elongated reflections along the edges of the structural components defining the gap, the gap width can be measured at various measurement points along the elongated reflections. The travel of the gap can then be determined from the discrete measurement points.
The device in accordance with the invention uses elongated reflections at the edges of the structural components defining the gap. These reflections are caused by the light beams emitted by the illumination means. One can, however, also use illumination means having elongated light sources which are reflected at the edges. In this case, the elongated reflections received by the detection means represent the reflected image of the illumination means at the edges of the structural components defining the gap.
In accordance with an advantageous further development of the present invention, the illumination means are oriented relative to the gap such that the light beams of the illumination means impinge on the edges of the structural components at an angle of  less than 90xc2x0 with respect to an imaginary tangential plane, extending along the gap of the structural components, in particular at an angle of between 30 to 60 degrees. It has turned out that particularly accurate measurement results can be achieved if the illumination means are oriented with respect to the gap in such a manner that the light beams impinge on the edges at an angle of approximately 45xc2x0 with respect to the tangential plane.
To guarantee uniform illumination of the two edges defining the gap, a preferred embodiment proposes that each illumination means illuminates the edge disposed on the other side of an imaginary normal plane extending orthogonally to the tangential plane and through the gap. In this manner, the illumination means illuminate the edges in a cross-wise manner. The illumination means on the left-hand side of the normal plane illuminate the edge on the right-hand side and the illumination means on the right-hand side illuminate the edges on the left-hand side of the normal plane.
Advantageously, the illumination means comprise at least two light sources of which at least one is disposed on one side of the normal plane and at least one on the other side of the normal plane.
In accordance with a preferred embodiment of the present invention, the or each light source comprises at least one light emitting diode (LED). LEDs have the advantage that they are very small, have a relatively large illumination strength and exhaust very little heat during operation.
In an advantageous manner, the or each light source comprises several LEDs disposed in at least one row. The or each light source advantageously comprises several rows of LEDs, wherein the LEDs are disposed in a row offset to the LEDs of a neighboring row. This ensures that the LEDs generate a line-shaped reflection at the edges of the structural components and not a sequence of several dot-shaped reflections.
In a preferred embodiment of the present invention, the illumination means emit light in the infrared (IR) range. This light is not visible to the human eye. The illumination means comprise appropriate display means to indicate operation and proper function of the illumination means. These display means constitute e.g. LEDs of different colors or a liquid crystal display (LCD).
In an advantageous further development of the invention, the illumination means emit light pulsed at a certain pulse cycle rate to facilitate proper operation of the inventive device irrespective of ambient light conditions (e.g. sunlight or artificial light in buildings). The detection means also receive the line-shaped reflections at the edges of the structural components at a certain pulse cycle rate. Advantageously, the illumination means and the detection means operate at the same, synchronized pulse cycle rate.
In an additional advantageous embodiment of the invention, the detection means are oriented relative to the gap such that the detection means view the edges of the structural components at an angle of  less than 90xc2x0 with respect to the imaginary tangential plane, in particular at an angle of 30 to 60xc2x0. It has turned out that particularly precise measurement results can be achieved by orientation of the detection means relative to the gap such that the edges are viewed at an angle of approximately 45xc2x0 with respect to the tangential plane.
In accordance with a preferred embodiment of the invention, the detection means comprise at least two video cameras of which at least one is disposed on one side of the normal plane and at least one on the other side of the normal plane. Video camera arrangement of this kind permits reliable measurement of the width of the gap, largely independent of the surface quality of the structural components.
Advantageously, the or each video camera comprises a charge-coupled device (CCD) image converter. Alternatively, video cameras with CMOS (complementary metal oxide semiconductor) image converters can also be used.
In order to carry out three-dimensional measurements of the transition from one structural component to the neighboring structural component, a preferred embodiment proposes that the detection means comprise two video cameras, wherein the evaluation means combine the images of the video camera to form a three-dimensional image. Each video camera records a two-dimensional image. The evaluation means can combine the two two-dimensional images into a three-dimensional image when the exact position and orientation of the two video cameras is known. For correct superposition, previous calibration of the video cameras has to be carried out. This can be effected e.g. using a known calibration object. The three-dimensional image can be used to also measure the offset of the two structural components in addition to the width of the gap between the two structural components. In the context of the invention, offset refers to the height difference between the surfaces of the two structural components in the gap region.
The evaluation means is preferably a computer, in particular an industrial PC. The computer can assume process control of the entire gap measurement and appropriately control the illumination means and the detection means. For integration of the device in accordance with the invention into a higher ranking device, the computer can receive appropriate control commands from a higher ranking control unit, e.g. for starting gap measurement at a certain point in time.
Measurement of the width of the gap by the device is preferably effected in real time.
The illumination means and at least two video cameras can be combined into a measuring head arrangement. The illumination means and the video cameras are mounted within the measuring head arrangement and oriented for a fixed, delimited measuring range. The measuring range comprises a three-dimensional measuring volume, in which the measuring head arrangement can carry out measurement with maximum accuracy or in which measurement is generally possible. It is e.g. feasible that the video cameras cannot thereby detect any line-shaped reflections on the edges of a gap located outside of the measuring range.
The measuring head arrangement must only be positioned and oriented such that the gap to be measured is within the predetermined measuring range of the measuring head arrangement. Such a measuring head arrangement is particularly easy to handle when it constitutes one single unit. The entire measuring head arrangement can be mounted on a robot arm and moved by the robot to a certain position and location so that the gap to be measured is within the measurement range. A measuring head arrangement can also be a hand-held device which can be manually positioned by a user into a certain orientation and location such that the gap to be measured is within the measuring range of the measuring head arrangement.
The device advantageously comprises means for changing the position and/or the location of the illumination means and the video cameras relative to the gap and means for fixing the illumination means and the video cameras at a certain position or location. These means may e.g. constitute a manually adjustable hinged arm with at least six different positions.
In accordance with a particularly preferred embodiment of the present invention, the device is a gap measuring device for measuring the gap width between the leaves or the rest of the body of a vehicle.
A further object of the present invention concerns the construction and development of a gap measuring arrangement of the above mentioned kind, wherein the gap width between the leaves or the rest of the body of a vehicle can be measured in a simple, reliable, precise, reproducible manner and independently of the surface finish of the body.
In achieving this object, the invention departs from the gap measuring arrangement of the above mentioned kind such that the gap measuring arrangement comprises several devices arranged about the vehicle and oriented towards the gaps at predetermined positions and locations. The gap measuring arrangement in accordance with the invention permits measurement of the gap width between the leaves or the rest of the body of a vehicle, independent of the surface finish of the body. The gap measuring arrangement provides reliable and exact measuring results, independent of whether the surfaces of the body are untreated and mat or painted, and independent of the color of the surfaces.
In an advantageous further development of the present invention, the devices are disposed inside of a tunnel-like supporting frame. The supporting frame is at least large enough to receive part of a vehicle. The supporting frame comprises curved supporting elements and transverse beams releasably mounted thereon. The devices are preferably mounted to the transverse beams and can be easily removed, together with the transverse beams, from and re-inserted into the supporting frame. The releasable connections between the transverse beams and the supporting elements are formed such that the transverse beams automatically assume their position relative to the supporting elements during insertion into the supporting frame. The positioning accuracy is a few millimeters, preferably less than one millimeter. The gap measurements are carried out with the vehicle disposed within the supporting frame.
Advantageously, there may be relative motion between the vehicle and the devices. The vehicles on production lines are guided through the supporting frame. The devices inside of the supporting frame either follow the motion of the vehicles, at least for a certain period of time, or are stationary and carry out the gap measurements when the corresponding gap of the vehicle is within the fixed measuring range of a device.
In accordance with a preferred embodiment of the invention, the devices remain stationary on the supporting frame and the vehicle moves through the supporting frame.
Advantageously, at least one device sequentially measures the width of at least two gaps. In this manner, the number of required devices can be reduced for a given number of measuring points at which the gap width is to be measured.
The evaluation means of several devices are preferably combined into a common evaluation unit to reduce the number of evaluation means for the inventive gap measuring arrangement.
The position of the devices within the supporting frame is preferably selected such that a gap of at least 30 centimeters, preferably approximately 50 centimeters, remains between the vehicle and the devices to prevent clamping of persons or body parts between the devices and the vehicle moved through the supporting frame.
A further object of the present invention is to design and further develop a method of the above mentioned kind such that the gap width between two structural components can be measured in a simple, reliable, exact, and reproducible fashion, independent of the surface finish of the structural components.
In achieving this object, the invention departs from a method of the above mentioned kind by detecting line-shaped reflections at the edges of the structural components and by detecting the gap width by evaluation of the detected reflections.
A dark/light/dark transition between the line-shaped reflections at the edges of the structural components defining the gap is advantageously detected.
In an advantageous further development of the invention, mismatch between two structural components is detected. Mismatch refers to the height difference between the surfaces of the two structural components with respect to one another in the region of the gap.
The width of the gap and/or the mismatch is advantageously measured in real time. The measurement of the width of the gap and/or of the mismatch comprises detection of the line-shaped reflections by the detection means, evaluation of the detected reflections and determination of the width of the gap and the mismatch with the evaluation means.
According to a preferred embodiment, several images are recorded of the line-shaped reflections at the edges of the structural components in rapid time sequence, wherein the recorded images are buffered and the width of the gap and/or the mismatch is determined by evaluation of the images.
In an advantageous manner, the measuring values extracted from the recorded images are filtered and/or statically evaluated. The measuring values extracted from the recorded images are preferably averaged. In addition, the plausibility of the measuring values extracted from the recorded images can be checked. Unplausible measuring values are not taken into consideration for determination of the gap width or mismatch. Measuring values having large deviations can e.g. be sorted out within the scope of the plausibility check.
A preferred embodiment of the present invention is illustrated in more detail below with reference to the drawing.